Various types of oxygen sensors have been proposed; in one such construction, a solid electrolyte, essentially tubular element in which the tube is closed at one end, has an outer sensing electrode exposed to the test gases, typically exhaust gases from an internal combustion (IC) engine applied thereto; a second electrode is located at the inner portion of the hollow tubular element, which is exposed to air, the oxygen of which forms a reference gas with respect to oxygen content in the exhaust gases from the IC engine. Preferably, the outer electrode is catalytically active (see German Patent Disclosure Document DE-OS No. 23 44 245, for example).
It has been found that, in use, a certain shift in the signal voltages will result, particularly in a direction to lower signal voltage levels. If such a sensor is included in an automatic fuel-air mixture control system, optimum supply of fuel to the IC engine may be impaired. The sensors may, in cross section, be essentially ring-shaped; the space to which the reference electrode, that is, the electrode exposed to the oxygen of ambient air is placed, need not be cylindrical or quasi-cylindrical, however; the space or chamber may have any other cross section, for example rectangular--see U.S. application Ser. 121,632, filed Feb. 14, 1980 now U.S. Pat. No. 4,282,080 Muller et al. The chamber, further, may retain a heating element therein, see for example the aforementioned U.S. application Ser. No. 121,632, now Patent 4,282,080 Muller et al U.S. Pat. No. 4,212,720, filed June 27, 1978 or U.S. Pat. No. 4,219,399, filed Sept. 10, 1979 Sensors may operate in accordance with the potentiometric principle, that is, similar to a fuel cell, or according to the polarographic principle (see U.S. application Ser. No. 213,049, filed Dec. 4, 1980, DIETZ, now U.S. Pat. No. 4,356,065).